The present invention relates generally to suspension systems for isolating and reducing the transmission of vibratory motion between an object or payload and a base and, more particularly, to a compact vibration isolator which exhibits low stiffness in the direction of the weight load to effectively reduce the transmission of vibrations between the object and the base. The present invention represents improvements over my previous isolators which utilize negative-stiffness mechanisms to produce low vertical natural frequencies and which rely on a principle of loading a particular elastic structure which forms the isolator or a portion of it to approach the elastic structure's point of elastic instability.
The problems caused by unwanted vibration on equipment, devices and processes that are extremely motion sensitive have been widely researched and numerous solutions to prevent or reduce the transmission of vibratory motion have been proposed and developed. Many of the devices designed to reduce the transmission of unwanted vibration between an object and its surroundings, commonly called vibration isolators or suspension devices, have utilized various combinations of elements such as resilient pads made from a variety of materials, various types of mechanical springs, and pneumatic devices. There are, however, shortcomings and disadvantages associated with these particular prior art isolation systems which prevent them from obtaining low system natural frequencies and from limiting internal structural resonant responses to low values while providing high isolation performance at the higher frequencies.
These shortcomings and disadvantages of prior art systems were addressed through the development of novel vibration isolation systems devices described in U.S. Pat. No. 5,530,157, entitled “Vibration Isolation System” issued May 10, 1994, U.S. Pat. No. 5,370,352, entitled “Damped Vibration System” issued Dec. 6, 1994, U.S. Pat. No. 5,178,357, entitled “Vibration Isolation System” issued Jan. 12, 1993, U.S. Pat. No. 5,549,270, entitled “Vibration Isolation System” issued Aug. 27, 1996, U.S. Pat. No. 5,669,594, entitled “Vibration Isolation System” issued Sep. 23, 1997, U.S. Pat. No. 5,833,204, entitled “Radial Flexures, Beam-Columns and Tilt Isolation for a Vibration Isolation System issued Nov. 10, 1998, and Improved Vibration Isolation Systems, Ser. No. 13/587,135 filed on Aug. 16, 2012, which are all hereby incorporated by reference in this present application. These vibration isolators exhibit low stiffness, high damping to limit resonant responses of the composite system, effective isolation at the higher frequencies, and can provide high isolator internal structural resonant frequencies.
The particular vibration isolation systems described in these patents provide versatile vibration isolation by exhibiting low stiffness in an axial direction (generally the direction of the payload weight) and any direction substantially transverse to the axial direction (generally a horizontal direction), and may provide tilt or rotation about three mutually perpendicular axes. The present invention, however, is directed only to isolators used to isolate vibratory motion in the axial or vertical direction. It should be appreciated, however, that the present invention could be connected in series with a horizontal-motion isolator and/or a tilt-motion isolator to provide bi-directional or omni-directional isolation as well. In subsequent discussions, an axial-motion isolator will be referred to as a vertical-motion isolator, and a system using multiple axial-motion isolators will be referred to as the vertical-motion isolation system.
In the embodiments described in the above-noted patents, the isolators rely on a particular principle of loading a particular elastic structure which forms the isolator or a portion of it (the loading being applied by either the supported weight or by an external loading mechanism) to approach the elastic structure's point of elastic instability. This loading to approach the point of elastic instability, also called the “critical buckling load” of the structure, causes a substantial reduction of either the vertical or the horizontal stiffness of the isolator to create an isolation system that has low stiffness in the vertical and in any horizontal direction, and increases the damping inherent in the structure. While stiffness is reduced, these isolators still retain the ability to support the payload weight.
In the event that the load on the elastic structure is greater than the critical buckling load, the excessive load will tend to propel the structure into its buckled shape, creating a “negative-stiffness” or “negative-spring-rate” mechanism. By combining a negative-stiffness mechanism with a spring, adjusted so that the negative stiffness cancels or nearly cancels the positive stiffness of the spring, one obtains a device that can be placed at or near its point of elastic instability. The magnitude of the load causing the negative stiffness can be adjusted, creating an isolator that can be “fine-tuned” to the particular stiffness desired.
These above-described isolators provide excellent devices for isolating or reducing the transmission of vibratory motion between an object and the base. It would be particularly beneficial if such vertical-motion isolators which rely on this principle of loading the structure to approach its point of elastic instability could be made in a more compact size and shape which may be more suitable for certain vibration isolation applications. While a more compact geometry would be beneficial, it is important that the performance of such vertical-motion isolators not be compromised. The present inventions solve these and other needs.